1. Field of the Invention The present invention relates to a mold clamping mechanism for an injection molding machine and, more particularly, to the prevention of a tilt of a rear platen constituting a part of a mold clamping mechanism.
2. Description of the Prior Art
For an injection molding machine, mold opening/closing and mold clamping are performed by moving a movable platen to which a movable-side mold is attached toward a fixed platen to which a fixed-side mold is attached. During the time when the movable platen moves toward the fixed platen, the surface of the movable-side mold must be in parallel with the surface of the fixed-side mold. For this purpose, the movable platen must move in a posture parallel with the fixed platen. If the parallelism between the movable platen and the fixed platen breaks down, the parallelism between the fixed-side mold and the movable-side mold is naturally lost, which exerts an influence on the accuracy of molded product.
Thereupon, in order to obtain a molded product with high-accuracy, it is necessary to maintain the parallelism of the movable platen with the fixed platen and to restrain the loss of parallelism in the mold opening/closing operation.
To restrain the loss of parallelism, a method has conventionally been used in which the tilt of the movable platen in the advance direction is corrected by adjusting a roller, a sliding bearing, or the like that supports the movable platen, by which the parallelism between the movable platen and the fixed platen is maintained.
For a toggle type mold clamping mechanism using a toggle mechanism, in order to maintain the parallelism between the movable platen and the fixed platen with higher accuracy, it is necessary to correct the tilt of a rear platen in addition to the tilt of the movable platen.
The position of center of gravity of the whole of the rear platen and the toggle mechanism shifts to the movable platen side due to the influence of a toggle mechanism component such as a toggle link constituting the toggle mechanism. Therefore, the rear platen is prone to tilt to the movable platen side. This tilt of the rear platen exerts an influence on the tilt of the movable platen via the toggle link and tie bars that are provided between the fixed platen and the rear platen to guide the movable platen. Also, if the tilt of movable platen is corrected forcibly by the roller, the sliding bearing, or the like that supports the movable platen in a state in which the rear platen tilts, the parallelism between the rear platen and the movable platen breaks down, so that an unbalanced load acts on the tie bars and the toggle mechanism, and thus partial wear is liable to occur. As a result, the parallelism between the fixed platen and the movable platen breaks down.
A method is known in which an eccentric shaft that supports the movable platen on a bearing fixed to a linear guide unit is provided, and the tilt of movable platen is adjusted by this eccentric shaft. Also, a method of adjusting the rear platen in the same way as the adjustment of the tilt of movable platen is also known (refer to Japanese Patent-Application Laid-Open No. 9-262884).
As described above, the tilt of rear platen resultantly exerts an influence on the parallelism between the movable platen and the fixed platen. Therefore, in the case where the tilt is corrected by the linear guide unit and the eccentric shaft as described in Japanese Patent Application Laid-Open No. 9-262884, there arises a problem in that the linear guide unit becomes large and complicated. The linear guide unit is required to have a construction enough to withstand a vertical load caused by the deformation of the rear platen at the time of mold clamping. For this purpose, the linear guide unit must have a large size and a complicated construction, which increases the cost. The use of linear guide unit can be thought for a component that moves at a high speed like the movable platen. The aforementioned Publication describes the adjustment of the tilt of movable platen using the linear guide unit and the eccentric shaft, and merely describes the additional applicability of this adjusting method to the rear platen. However, since the rear platen does not move at a high speed, there is little need for using the expensive linear guide unit.